Grassholm is a tiny island, just 200 metres across, located 15 kilometres off the southwest Pembrokeshire coast. Owned and managed by the RSPB, the island is home to one of the largest gannet colonies in the entire world supporting 39,000 breeding pairs, some 9.5 % of the world’s population. Yet despite its remote location, recent ground survey by Commission staff Olly and Louise has revealed the traces of roundhouses and field boundaries indicating that this tiny island was also once home to a thriving prehistoric community!

The Royal Commission first surveyed the island back in 1972 – Commission Investigator Douglas Hague visited the island and planned and excavated the remains of a small settlement of conjoined rectangular buildings. This was situated on the western side of the island where the caustic effect of gannet guano had killed the dense mattress of grass exposing the archaeological remains beneath. The settlement appeared similar to structures identified on nearby Gateholm and were presumed to be Medieval – perhaps even representing the ‘lordly hall’ mentioned in the legend of Branwen in the Mabinogion.

Hague’s settlement has now been covered over by gannet nests which crowd onto the western side of the island. But, as the gannet colony has expanded in size, increasingly more of the island’s archaeology is being revealed. Aerial reconnaissance by the Commission in 2011 identified what looked like the remains of prehistoric occupation running down the central spine of the island. This needed verification on the ground and the Commission was fortunate enough to be offered an opportunity to do just that, by accompanying the RSPB on their annual Grassholm rescue mission to cut free gannet fledglings tangled up in marine debris.

The trip out to the island was exciting – dolphins and seabirds accompanied us on our hour long journey in a small RIB from St Justinians. Once we reached the island, there are no beaches, so to disembark from the RIB we had to scramble up the shallow sloping cliffs. The first thing you notice is the smell – the guano of nearly 80,000 gannets fills the air with a potent scent, but the magical landscape of the island more than makes up for that.

The gannets watch an archaeologist surveying the island’s remains.

The western side of the island is covered in gannet nests – squat pillars of mud, stained white from guano – while the eastern side is covered by tussocky grass. But, a narrow strip of ground within the centre of the island, running from the north to south coast is free of both nests and grass and it’s here that the archaeological remains were most visible.

What we found was extraordinary. The remains of two small roundhouses, barely 4m in diameter, were visible. The tumbled walls of field boundaries radiated out from them forming small fields, terraces and garden plots. Clearly this was a serious attempt to set up a small farmstead and the remains reminded us of similar structures identified on nearby Skomer. There was also what appeared to be cairn – a mound of stones, perhaps simply the result of field clearance, but it could also mark the burial place of one of the island’s prehistoric inhabitants.

One of the small stone-built roundhouses identified during the survey.

We didn’t get long on the island – perhaps only a couple of hours before the tide and swell meant we had to leave – but what we discovered has changed our understanding of this remote place. The structures we surveyed are almost certainly prehistoric and clearly very different in character to those planned and excavated by Hague more than 40 years ago. It seems then that we have at least two phases of occupation on the island, perhaps in both the Iron Age and early Medieval periods, but it’s hard to imagine people living on this isolated and remote island permanently or for any lengthy period of time – perhaps the occupation was only seasonal to catch seabirds or de-pasture sheep. Hopefully more research and further visits in future years will provide us with more clues about the occupation and exploitation of this enigmatic little island.

With huge thanks to the RSPB for allowing us the opportunity of visiting the island and to Tim and Beth from Venture Jet for getting us there and back safely.

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